The wooden cill that forms a watertight seal against the top gate has been damaged by a boat to such an extent that the gate cannot seal, preventing navigation. British Waterways staff have put stop planks in place to prevent the pound above draining.
On the morning of Thursday 14th April BW staff will remove the stop planks and assist waiting boaters through the lock. At 10.00 am the stop planks will be put back in place and the wooden cill will be replaced. The lock will closed until the repair is complete, possibly for the rest of the day.
There is currently a leak on the pound above this lock, which BW is trying to locate and which is causing the pound to become low. Unfortunately the level was too low for the boat to cross the cill block without causing damage.
Update, 14th March 3.30 pm: The repair has now been completed and the canal has re-opened to navigation.
Lock 12e at Milnsbridge
Note concerning cills:
Boaters should be aware that, when closed, a lock gate butts up to a wooden cill (or threshold) that forms a water-tight seal against the gate. These wooden cills are usually slightly higher than the adjacent canal bed. Attempting to enter or leave a lock when water levels are too low can result in the boat's skeg catching the cill and damaging it, or even ripping it out of place.
This will mean a water-tight seal cannot be made, making it difficult (or impossible) to completely empty or fill the lock.
When levels are low, boaters should proceed slowly and be prepared to stop and back off it the boat makes contact with the wooden cill. Forcing the boat over a cill is selfish and could result in other boaters having their holidays spoilt by a stoppage. The best course of action is to send someone to open the next paddle above the cill in question and wait until water levels are high enough to cross a cill without making contact. (Only enough water should be released to increase the water level sufficiently. The paddle should then be closed again to prevent the pound above also becoming too low.)